This invention relates to a secondary communication equipment for use in a data communication or transmission network between a pair of primary communication equipments. The primary and secondary communication equipments are installed in primary and secondary stations. Therefore, the primary and the secondary communication equipments may alternatively be called the primary and the secondary stations.
In the manner which will later be described with reference to a few of nine figures of the accompanying drawing, a known data communication network comprises a pair of primary communication equipments and a series of secondary communication equipments between the primary communication equipments. The primary and the secondary communication equipments are connected together by a pair of unidirectional data channels or lines. Each primary communication equipment is for successively transmitting signal combinations at a predetermined time interval through a pertinent one of the data channels. Each secondary communication equipment comprises a receiver for detecting, among other, a flag in each signal combination and a transmitter coupled to the receiver for transmitting, upon detection of the flag, a combined signal which comprises the flag and a data signal which should be transmitted from the secondary communication equipment under consideration towards a particular one of the primary communication equipments.
In the known data communication network, each primary communication equipment collects such data signals from the series of secondary communication equipment. When a fault occurs in one of the data channels that transmits the data signals to the particular primary communication equipment, the flag does not reach those of the secondary communication equipments which are downstream from a point of the fault in the data channel in question. It is impossible for either of the primary communication equipments to collect the data signals from the series of secondary communication equipments.